1. Field of the Invention
The present invention relates to an image stabilizing apparatus which is disposed within an optical apparatus such as monocular, binocular, or video camera in order to prevent optical images from being blurred upon viewing when the angle of emission of a luminous flux from the viewed object with respect to the optical axis of such an optical apparatus fluctuates upon vibration.
2. Description of the Prior Art
In cases where an optical apparatus, such as monocular or binocular, aimed for optical viewing is operated as being held with a hand, in particular when the optical apparatus is used as being brought into an airplane, vehicle, or the like, vibration or rolling of the airplane, vehicle, or the like is transmitted to the optical apparatus, whereby the angle of emission of the luminous flux from the viewed object with respect to its optical axis is likely to fluctuate. As a result, the viewed optical image often deteriorates. Even when such a vibration transmitted to the optical apparatus has a small amplitude, the angle of fluctuation with respect to the optical axis is magnified since the monocular, binocular, or the like has a narrow visual field and magnifies the object upon viewing. Hence, the viewed image may move fast in the visual field even upon rolling with a relatively low speed of angular fluctuation, and it may deviate from the visual field when the angle of fluctuation is large. Also, upon rolling with a relatively high speed of angular fluctuation, even when the angle of fluctuation is relatively small, the viewed object has a higher speed of angular fluctuation in response to the magnification of the optical apparatus, whereby the image may blur and deteriorate.
There have conventionally been proposed various kinds of image stabilizing apparatus for preventing a viewed image from deteriorating due to fluctuation in the angle of emission of a luminous flux with respect to the optical axis upon vibration or rolling transmitted to the optical apparatus.
For example, Japanese Patent Publication No. 57-37852 discloses a binocular comprising a vibration isolator therein utilizing a rotational inertial body (gyro motor) in order to correct blur of the viewed image in the binocular.
Namely, in this prior art, an erecting prism is disposed on the optical axis between objective and ocular lenses of the binocular so as to be secured onto gimbal suspension means to which the rotational inertial body is attached, whereby the erecting prism is substantially held in the same posture even when the binocular is vibrated upon a manual shake or the like, so as to prevent the viewed image of the binocular from blurring.
In such a kind of prior art utilizing the rotational inertial body and the gimbal suspension means, while the image can be stabilized with a high precision, a high-speed rotator is necessary for obtaining a large inertial force in a small space. Also, the rotator should have a high precision since it is necessary for the rotator to minimize its own vibration. Due to these requirements for small size, high speed, and high precision, the apparatus may become disadvantageous in terms of cost, life, and time necessary for obtaining a required inertial force after the power is turned on. Also, when the effective diameter of the objective lens is increased in order to attain a higher magnification or resolution in the binocular, the erecting prism has a larger size, thereby necessitating a larger inertial force. Consequently, the disadvantages noted above may become greater. Also, a larger amount of electric power may be consumed accordingly.
Therefore, there has been proposed a commonly-assigned image stabilizing apparatus Japanese Unexamined Patent Publication No. 6-250100) in which the gimbal suspension means is equipped with an angular velocity sensor in place of the above-mentioned rotational inertial body, while the rotational position of the gimbal suspension means is controlled on the basis of the output value from the angular velocity sensor so as to secure the posture of the erecting prism with respect to the earth (inertial system). In this apparatus, the erecting prism held by the gimbal suspension means basically has an inertial force and, for high-speed vibrations with a high frequency in particular, exhibits a high performance for holding a posture against a vibration with a relatively large amplitude. Accordingly, a small force is sufficient for controlling the rotational position based on the output from the angular velocity sensor.
Variangle prisms and other kinds of image stabilizing apparatus which drive lenses, however, necessitate an active driving section. Since it is necessary for the driving section to be moved with a high speed in order to correct a large amplitude in high-frequency vibrations, such an amplitude is hard to correct over a large angle range.
Also, in the above-mentioned image stabilizing apparatus for securing the posture of the erecting prism with respect to the earth (inertial system) by controlling the rotational position of the gimbal suspension means, there is a possibility that the gimbal suspension means might be mechanically locked at a position other than its standard position due to an external shock, a failure, or the like.
In this state, when the control system is kept operable as it is, an electric power may be supplied in excess to an actuator such as driving motor in order to return the gimbal suspension means to the standard position, thereby damaging the actuator.
Also, while a control loop is constituted by electric devices such as CPU in the above-mentioned control system, when a driving voltage supplied to such an electric device, CPU in particular, is lowered, the control system may not function correctly, thereby causing a malfunction. As a result, even when the optical apparatus is directed to the aimed object to be viewed, another object positioned in a direction different therefrom may be observed.